1. 1. Field of the Invention
The invention relates to a method of activating chemical compositions in which one or more of the active ingredients is microencapsulated by ultrasonically rupturing the microcapsules. The method is particularly suitable for activating adhesive, sealant or coating compositions.
2. Description of Related Art
It is known to incorporate microencapsulated active ingredients in such compositions. Active ingredients would include, for example, resins and monomers as well as primers, activators, accelerators or initiators. For example, German Pat. No. 2,023,999 and U.S. Pat. No. 3,826,756 teach microencapsulation of certain scrylic monomers; German Pat. No. 2,629,889 teaches microencapsulation of ferrocene activators; Japanese U.S. Pat. No. 85/07,931 discloses microencapsulation of acrylic monomers by photpolymerization techniques; German Patent No. 3,401,056 discloses microencapsulation of solvent activators for adhesives; Japanese Pat. No. 84/01,506 discloses microencapsulation of latent hardeners for epoxy adhesives; European Pat. No. 63,475 discloses microencapsulation of cross-linking agents for epoxy adhesives; Japanese Pat. No. 82/12,039 discloses microencapsulation of certain catalysts for polymerization of acrylic monomers; Japanese Pat. No. 78/31,579 and Japanese Pat. No. 81/100,631 disclose microencapsulation of cross-linking agents for polyisocyanates; Japanese Pat. No. 76/147,539 discloses microencapsulation of an ethylene-vinyl acetate copolymer adhesive; U.S. Pat. No. 3,839,220 discloses microencapsulation of fluorocarbons together with reagents for epoxy and polyamide adhesives and coatings German Pat. No. 2,308,850 discloses microencapsulation of liquid anaerobic compositions; and U.S. Pat. No. 4,293,677 discloses microencapsulation of organo- hydrogenpolysiloxane reagents for silicone adhesives and coatings.
It is usual to use physical pressure for rupturing such microscapsules to release the active ingredient, thereby rendering the entire composition active.
The use of high-intensity ultrasound for rupturing the walls of biological cells has been known for a substantial number of years. However in the field of polymer chemistry, the principal industrial use of ultrasound has been for welding of thermoplastic materials.
Japanese Pat. No. 82/63,895 of Tokyo Denki Kagaku Kogyo Co. Ltd. discloses a method for mounting an electronic chip component on a printed circuit board using an adhesive composition which has its curing agent sealed into microcapulses. When the electronic chip component is mounted on the printed circuit board, with the adhesive composition between them, the microcapsule is ultrasonically pulverized to activate the adhesive.
However the method of Japanese Pat. No. 82/63,895 involves the application of ultrasonic oscillations to the solid chip component, through which the oscillations are transmitted to the adhesive composition. The present inventors have found that this method which involves indirect application of ultrasound through a rigid substrate is not generally applicable to other substrates and frequently leads to unsatisfactory bonds. Furthermore the application of ultrasonic oscillations to a rigid chip component or substrate is likely to result in an uncomfortable level of audible sound.